Method of making an electrode grid



Nov. 4, 1969 P. FABER METHOD OF MAKING AN ELECTRODE GRID Filed Sept 15,196'? 2a. Graphi ized carbonaceous Filament Pe fer Fabe INVEN'TOR.

United States Patent 3,476,604 METHOD OF MAKING AN ELECTRODE GRID PeterFaber, Kahl am Main, Germany, assignor to Rheinisch-WestfalischesElektrizitatswerk Aktiengesellschaft, Essen, Germany, a corporation ofGermany Filed Sept. 15, 1967, Ser. No. 668,006 Claims priority,application 2G2'e7rmany, Sept. 29, 1966,

Int. Cl. noim 35/04 US. Cl. 136-36 6 Claims ABSTRACT OF THE DISCLOSUREMy present invention relates to a grid for an electrode of anelectrochemical cell, e.g. a fuel cell or a unit of a primary orsecondary battery. Such grids serve the dual purpose of supporting theactive electrode material and provide a low-resistance current pathbetween the particles of such material.

An object of this invention is to provide a grid of this descriptionwhich, taken by itself or when loaded with active electrode material,constitutes a porous body of large effective surface and low specificweight.

It is also an object of this invention to provide a simple and efiicientmethod of producing such a body.

These objects are realized, in accordance with my present invention, byutilizing a web of carbonized and at least superficially graphitizedfilaments as a coherent skeleton on which a metallic coating isdeposited to confer the necessary rigidity and conductivity upon theweb. The metallic coating may be deposited from a suitable metalizingbath, with or without the application of a galvanizing voltage.Advantageously, this coating consists predominantly of nickel, thepresence of a small proportion of boron (e.g. of about by weight) in thecomposition being preferred. A coating of this description can bedeposited, for example, from an aqueous solution of a nickel salt (e.g.NiCl or NiNO in the presence of a reducing boron compound (e.g. aborohydride such as LiBH Metalization by a simple redox process, withoutapplied voltage, results in a substantially uniform distribution of themetallic deposit; the use of an electrolytic plating process, on theother hand, may lead to a denser deposit near the outer boundaries ofthe web which will usually not be objectionable.

Particularly with a nickel-containing coating, a thickness of about 5 toa for the metallic layer has been found very satisfactory.

The web of carbonaceous filaments to be metalized may be produced bycharring a fabric or felt of cellulosic fibers and thereafter heatingthese fibers to a temperature on the order of 2000 C. for a timesuflicient to result in at least superficial graphitization thereof. Thecharring step may 3,476,604- Patented Nov. 4, 1969 be carried out in anevacuated heating chamber or in a protective atmosphere.

Carbonaceous and graphitized filaments so obtained may have an overallthickness, together with their metallic coating, ranging between about10 and 20 The plateshaped web itself may be originally up to 3.5 mm.thick, with a specific gravity of about 0.0 7 g./cm. and an elfectivesurface of up to 150 times its geometric area. The filaments may besintered together by their coating, in order to strengthen thestructure, by heating to a suitable temperature after metalization; thisis advantageously done, e.g. in vacuo or in an atmosphere of aprotective gas such as hydrogen, by the passage of a heating currentthrough the web whose conductive filaments form a continuous currentpath. If desired, the porous body so obtained may be further compactedin a press before, during or after the sintering process; the resultingplate may have a thickness of 1-2 mm., though higher degrees ofcompaction (down to a fraction of a millimeter) are also possible.

The grid so produced may be loaded with active material, e.g. nickelhydroxide, cadmium hydroxide, silver oxide or zinc, by conventionalprocesses such as pasting or vibration filling; this step may be omittedin the case of a fuel-cell electrode, e.g. for a cell of the air-zinctype.

The invention will be described in greater detail with reference to theaccompanying drawing in which:

FIG. 1 shows a web of metalized carbonaceous filaments forming part of agrid according to the invention;

FIG. 2 is a fragmentary perspective view of one of the filaments of FIG.1, drawn to a larger scale; and

FIG. 3 is a perspective view of a grid produced from the web of FIG. 1.

As shown in the drawing, a web 1 of metalized carbon filaments 3 isshaped into a rectangular plate having a terminal tab 4 attached theretoby spotwelding. As particularly illustrated in FIG. 2, each filament 3consists of an inner core 2a of carbon coated with a metal layer 2bpreferably having the aforedescribed composition of nickel and 5% boron.

A plate of this description is characterized by a surprising degree ofelasticity, especially when compared with conventional electrodes madefrom sintered granular particles with or without imbeddedreinforcements.

If a strip of felt or fabric of indefinite length is used to produce theweb of FIG. 1, charring and metalization may be carried out in acontinuous assembly-line-type process.

An electroless nickel-plating process of the type mentioned above hasbeen disclosed in US. Patent No. 3,338,741.

I claim:

1. A method of making a grid for an electrode of an electrochemicalcell, comprising the steps of carbonizing a web of cellulosic filaments,heating the carbonized web to a temperature on the order of 2000" C. forat least superficial graphitization, subsequently metalizing thefilaments so obtained to provide them with a metallic coating and alow-resistance current path, and sintering said filaments together attheir points of contact by passing an electric heating current throughsaid filaments so coated.

2. A method as defined in claim 1 wherein said coating consists at leastin major part of nickel.

3. A method as defined in claim 2 wherein said coating is a compositionof nickel and boron, the latter being present in a proportion ofsubstantially 5% by weight.

4. A method as defined in claim 2 wherein said coating has a thicknessranging substantially between 5 and 10 5. A method as defined in claim 4wherein said filaments have an overall thickness ranging betweensubstantially 10 and 20,u..

6. A method as defined in claim 1, further comprising the step ofcompacting said web of filaments.

References Cited UNITED STATES PATENTS Barnett 136-121 Basset 136-121Hartman et a1 136-64 10 Horn et a1 136-36 Haworth.

WINSTON A. DOUGLAS, Primary Examiner C. F. LEFEVOUR, Assistant ExaminerUS. Cl. X.R.

